1. Field of the Invention
The present invention relates to screw blowers and particularly to a screw blower for use with an internal combustion engine as a supercharger, to form a continuous exhaust flow, with minimal pulsation and smooth operation, and which can be operated at high efficiency with minimal power loss and torque fluctuation over a wide range of operating speeds from low speed to high speed. The blower is easily machined, and can be manufactured as a small and lightweight unit.
2. Description of the Prior Art
A blower or compressor is used as a means to feed gases, such as air or air-fuel mixture under pressure when supercharging is effected in order to increase the volumetric efficiency of the engine or when secondary air is supplied for purifying the exhaust gases. The conventional construction of a blower or compressor of this kind includes speed types including a centrifugal blower, an axial flow blower and the like, and volumetric types including a vane blower, a Roots blower, a screw blower and the like. In the blower or compressor, the speed type is suitable for operation at high speeds but is poor in efficiency at low speeds. Additionally, due to limitations in reductions in size and weight, application of the speed type is limited to specific fields. As regards the volumetric types, the vane type and the Roots type are suitable for low pressure compression and are high in efficiency at low speeds but are low in efficiency at high speeds, thus being unsuitable for high pressure compression. In addition, during operation, pulsations are liable to occur to produce noise, and the driving horse power and torque greatly fluctuate.
Additionally, in the screw type blower or compressor, the compression ratio can be selected easily, the efficiency during operation at high speed and high pressure is high, both suction and exhaust are continuous, pulsations are minimal and noise is also low. Fluctuation in driving horse power and torque is also small.